In the present work, the vasorelaxant effect of dioclein, a new flavonoid i
solated from Dioclea grandiflora (Leguminoseae), was investigated in the ra
t aorta. Dioclein induced a concentration-dependent relaxation in vessels p
re-contracted with phenylephrine (IC50 = 1.3 +/- 0.3 mu M), a response whic
h was abolished after endothelium removal. Neither indomethacin (10 mu M),
an inhibitor of cyclo-oxygenase, nor atropine (1 mu M), an antagonist of mu
scarinic receptors, modified the effect of dioclein. Dioclein (30 mu M) ind
uced a significant increase in guanosine 3':5'-cyclic monophosphate (cyclic
GMP) levels in aortic rings with endothelium. The nitric oxide (NO) syntha
se inhibitor, N-G-nitro-L-arginine-methyl-ester (L-NAME, 300 mu M), strongl
y inhibited or abolished the relaxing effect and rise in cyclic GMP levels
induced by dioclein. Furthermore, dioclein (30 mu M) had no effect on the e
ndothelium-independent relaxation produced by the NO donor, 3-morpholino-sy
dnonimine (SIN-1), while superoxide dismutase (100 U ml(-1)) significantly
potentiated it. These results indicate that, in the rat aorta, dioclein ind
uces a NO- and endothelium-dependent vasorelaxant effect, which is associat
ed with cyclic GMP elevation. This vasorelaxation likely results from enhan
ced synthesis of NO rather than enhanced biological activity of NO. (C) 199
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